1. Field of Invention
The present invention relates to an optical waveguide element.
2. Explanation of Related Art
A technology is disclosed that uses zirconia (ZrO2) as a dopant increasing a refractive index of an optical waveguide constituting a Planar Lightwave Circuit (PLC) element made of a silica-based glass (see Japanese Translation of PCT International Application Publication No. 2005-531030). ZrO2 is a material having a refractive index higher than that of Germania (GeO2) and a thermal expansion coefficient smaller than that of GeO2. For that reason, ZrO2 is expected to be a material that enables a PLC component or the like to be downsized and is capable of reducing a stress residing in a waveguide.
Conventionally, a technology is disclosed by which an optical waveguide containing ZrO2 is formed by using sol-gel method (see R. Sara et al. “Photolithography Fabrication of Sol-Gel Ridge Waveguide” SPIE vol. 3469 p. 118-123(1998), and S. Iraj et al. “Sol-Gel Glass Waveguide and Grating on Silicon” J. LIGHTWAVE TECH. VOL.16, NO.9, (1998) (hereinafter called Reference Literatures 1 and 2)).